基于virtual.labacoustics的倒l型声屏障降噪效果仿真分析机械设计制造开题报告大学论文
基于LMS Virtual.Lab扬声器频响计算
基于LMS b的扬声器频响计算背景介绍利用电-力-声类比电路的方法模拟喇叭单体或添加腔体情况下频响曲线的方法已经被大多数业界内学者专家所采用如利用广泛使用的T-S模型得到喇叭的机械、电声参数该方法对模拟喇叭单体自身频响比较准确，但是给喇叭添加前后音箱（手机内广泛采用）后就很难准确的模拟喇叭音箱模组的频响了根本原因：电声等效类比电路中，添加的腔体仅仅考虑了空腔的体积因素，而没有考虑腔体的形状因素，但腔体的形状对放入其内喇叭的频响有着重要的影响解决办法：通过3D 建模，采用有限元和边界元相结合的数值方法来模拟带前后音箱喇叭模组的频响曲线模拟对象模拟对象为广泛使用的1115 喇叭 其示意图如下：4版权LMS 国际-2006在b 中进行全耦合仿真的中进行全耦合仿真的全过程全过程载荷载荷（（频率的函数）膜片的模型/模态声学边界元声学边界元模型模型完全耦合振动声学模型完全耦合振动声学模型（（IBEM ）后处理结构特性的计算要进行声学性能计算，首先要计算音膜系统的模态 音膜第一、第二阶模态振形如下图所示带障板的计算工况在测量喇叭单体频响的时候都将喇叭安装在适当尺寸的障板上面来测量音膜振动是向前向后连续振动的，喇叭在向前辐射声音的同时也向后辐射，但是由于向前向后辐射的声音相差180 度相位，从而会导致后面的声绕到前面抵消掉前面的部分声能量在低频情况下最为明显仿真计算时也加上一块障板b可方便模拟带障板边界及消音室的边界得到仿真结果可与测试结果直接比较计算结果带障板状态下，计算得到的声场分布如下喇叭单体背面添加1cc 腔体喇叭前后的声场明显的分为两部分，向前辐射的声压大，向后辐射声压几乎为零喇叭音膜同时向前向后辐射声音，音膜前方敞开，声压能顺利的辐射出去，音膜背面有腔体封闭，因此音膜向后辐射的声压出不去，在腔体内部不断反射叠加，使得封闭腔体内部的声压最大障板工况与添加后声腔工况的计算结果比较从添加腔体前后的频响曲线看，增加1cc 腔体后，频响曲线的第一个峰值（这个峰值就是喇叭音膜的第一个共振模态）向高频移动喇叭背面添加1cc腔体后，喇叭音膜向后辐射的背压增大，相当于减小了弹性系统的顺性，增大了弹性劲度，因此振动系统的第一阶共振模态向高频移动了试验与仿真结果的比较仿真结果与测试结果的对比从喇叭单体和背面添加1cc 腔体两种情况下测试结果和仿真结果的对比来看，仿真结果和测试结果吻合的较好，差别在3dB以内总结仿真结果与测试结果的对比分析表明，仿真结果与测试结果的声压频响很接近，差别3dB 以内，这说明利用LMS b来模拟喇叭单体和添加背腔情况下的频响是可行的为喇叭单体的频响设计以及喇叭前后音箱的结构设计提供一种新的设计方法和手段。
LMSVirtualLabAcousticsA新功能介绍
L M S V i r t u a l L a b A c o u s t i c s9A版新功能介绍作者：LMSb是由以振动噪声、疲劳、操稳性工程解决方案着称的LMS际公司推出的全球第一个功能品质工程集成解决方案。
b提供集成的多学科软件平台用于分析和优化机械系统的性能，包括结构完整性，噪声及振动，耐久性，系统动力学，操稳性及平顺性、多体动力学以及其它属性。
b包括所有关键过程步骤及所需的技术，可以远在进行昂贵的加工和实物样机之前对每个关键属性进行从头到尾的评价，并使仿真设计真正迈向功能品质属性为目标的功能化设计，大大提升了仿真设计在产品开发中的功能性和指导性。
bAcoustics是b的拳头产品，是市场上最先进的振动声学和流体声学分析软件，从诞生开始多年来一直是声学领域排名第一的仿真软件，也是声学领域中公认的工业标准。
bAcoustics提供了从振动噪声到流体噪声，从声辐射到声-振耦合，从部件级到系统级，从低频到中高频，从前处理、求解器直到结果后处理的一个完整的解决方案。
在2009年11月正式推出的9A版本中，推出了开创性的有限元和边界元求解方案。
下面我们为大家做详细的介绍：完美匹配边界层技术：Fem-PMLbAcoustics9A版本中的FEM-PML完美匹配边界层有限元技术则在将有限元求解速度提高10+倍的同时，还极大地拓展了声学建模的灵活性和仿真应用范围。
FEM-PML技术通过在有限元模型外部建立声吸收层，可以完美解决有限元外场声辐射的问题。
FEM-PML技术不需要像无限元一样需要一个规则的外表面（球形或者椭球形），可以设定在离有限元模型非常接近的位置。
这样可以大大降低一般外场声辐射的模型自由度数，提高计算速度。
可以认为，FEM-PML是无限元的替代技术。
有限元/无限元搭建的发动机模型FEM-PML技术搭建的发动机模型拓展的快速多级边界元技术在8B版本中推出的FM-BEM快速多极边界元技术使得超大规模边界元模型的求解成为现实，并将分析频率范围直接拓展到高频：该模块运用迭代技术来求解边界元方程，通过基于多极扩展和多层次分级蜂窝子结构的高级算法，使得求解边界元方程的计算速度极大提高，同时内存消耗极大缩减。
LMS Virtual.Lab 电机噪声仿真计算
Flow-based
System
FEM-Acoustics
Receiver
Standard
Mechanical
BEM-Acoustics Advanced
Electro-magnetics
RAY-Acoustics
Test-based
SEA
4 Copyright LMS International - 2010
Electrical Motor EM noise Acoustic model
FEM Acoustics model
Valid up to:
8000 Hz
# nodes
12355
# elements
24 702 TETRA
HW
8CORE Win64
Calculation time
10 sec / frequency
Increasing strength of scattering effects
12 Copyright LMS International - 2010
Electrical Motor Electro-Magnetic Noise
Picture from JSOL
13 Copyright LMS International - 2010
High Fidelity System-level
High Fidelity Full System including the “environment”
3 Copyright LMS International - 2010
A systematic approach for N&V engineering
基于Virtual.Lab Acoustics的管道壁面声阻抗优化分析
Optimization and Analysis of Acoustic Impedance of Duct Wall Based on b Acoustics
Weiguang Zheng, Peng Xu, Zeyu Lin, Rongjiang Tang
School of Mechanical and Electrical Engineering, Guilin University of Electronic Technology, Guilin Guangxi
∫ [ N ] dΩ
其中 [ K ] 为声学刚度矩阵， [C ] 为声学阻尼矩阵， [ F ] 为声学激励。 在得到形函数的情况下，求解式(11)就可以得到节点处的声压。 为验证本文方法的准确性，采用文献[2]同样的模型。管道截面形状为正方形，边长取 0.066 m，管长 度取 1.2 m。管道内壁边存在两种边界条件，即刚性壁面条件与阻抗边界条件。在管道入口处施加单位速 度边界条件，出口施加无反射边界属性。管道壁面为刚性，声衬处采用法向阻抗边界条件。管道采用六 面体声学网格，网格大小为 6 mm，计算频率区间取 500 Hz 到 1500 Hz，网格单元数量为 2.42 万(图 2)。
法向阻抗边界条件 Ω z
(8)
p ∂p = − jρ0ω Zn ∂n
则
(9)
Ω = Ω r + Ωv + Ω z
(10)
和 p 具有相同的形函数，将式(4)与式(7)至式(10)代入式(6)中，经整理可得 假设 p
2 − jρ0ωun ∫ [ K ] + jρ0ω Z [C ] − k0 [C ] [ pi ] =
3.1. 声学仿真优化计算
模型的边界条件与优化参数的设置直接影响到声学仿真优化的准确性，本文采用 Tester [6]研究所得 的经验公式算出初始阻抗值，并在此基础上进行优化。以下表 1 与表 2 分别对应管内无流与有稳定切向 流两种情况下， 壁面最优声阻抗 Z (Z = Zo/ρ0c0， Zo 为最优阻抗值， ρ0c0 为空气特性阻抗， 本文取 416.5 kg/m2/s) 和传递损失，并将最优阻抗数值解与文献[5]的优化结果进行了对比(图 3)。
Virtual.lab声固耦合的隔声量仿真分析教程
FEM Direct Vibro-Acoustic Analysis Case Tutorial Objective:The goal of this tutorial is to calculate the acoustic response of a glass/PVB plate (a laminated safety glass with a Polyvinyl butyral layer in between).The tutorial includes using the following analysis cases:∙Structural Modal case∙Direct Structural Forced Response∙Direct Structural Vibro-Acoustic Response∙Transmission LossThe model contains a Visco-elastic frequency-dependent material.Pre-Requisites:Software Configurations that are needed to run the tutorial:∙Licenses to set up the case in LMS b: "Desktop (VL-HEV.21.1 or equivalent)"and "Finite Element Acoustics (VL-VAM.36.2)"∙When solving the acoustic response case, the license for product "LMS bFEM Vibro-Acoustics Structural Solver VL-VAM.45.2" is needed.∙Solving the Random Post-processing case to get the Transmission Loss curve willrequire the license for "Random Vibro Acoustic Analysis (VL-NVP.20.3)"Tutorial Data Files:StructuralGroups.xmlSAFyoung.xlsLaminatedStructure.bdfFPmesh.bdfAMLsender.bdfAMLreceiver.bdfAcousticGroups.xml[All data files can be found on the APPS n DOCS DVD, in an archive called VAM_DirectVA-TL. For ease of use, it is best to copy all files to a local folder.]STEP BY STEP Tutorial:STEP 1After starting LMS b, create a new document in the Acoustic Harmonic FEM Workbench (Start Acoustics Acoustic Harmonic FEM).STEP 2Select File Import from the main menu. [The Import command can also be selected from the contextual menu of the Links Manager, by right clicking]A file selector window appears allowing you to specify the file type and the file name. [For more details, see Importing Data]Select the file type NASTRAN Bulk File (*.bdf, *.NS, *.nas, *.dat) and browse for the file LaminatedStructure.bdf and click the Open button. A new dialog box appears requesting the selection of data that needs to be imported from the file. The data entries that are not available in the file are grayed out.Select in Split into Multiple Mesh Parts under Mesh Creation and set the unit system to Meter, Kilogram, Second, click the OK button.STEP 3Next, the different structural materials will be defined. The two outer layers of the panel are made of Glass. To incorporate the 2% structural damping of this material, it will be modeled asa viscoelastic material with a constant complex Young modulus. The inner layer is made of PVB.Insert Materials New Materials New Viscoelastic Material...[Right-click on the Materials feature in the Specification Tree New Materials New Viscoelastic Material]Define the materials as follows:The PVB material at the center of the windshield has strong frequency dependent stiffness properties and is nearly incompressible. The frequency dependency can be incorporated in a viscoelastic material using an edited load function. The values can be imported from the Excel document SAFyoung.xls as follows:Check Frequency Dependent, and right-click the input field.Select New Function.In the Attributes tab, enter as Name Young’s modulus PVB.In the Values tab, click the Import a file button, and browse to the excel file to select it.Switch the Data Format to Linear Amplitude/Phase (deg) because the file contains the values like that. Click the Import button.Click the OK button of the Function Editor GUI.Click the OK button on the Material GUI.On the Edited Load Function Set, create (using the context menu) a 2D display of type Complex(Edited Load Function) on the Young’s modulus and check the curve:STEP 4Defining two Structural 3D properties for Glass and PVB, applied to the structural groups Glass (with the defined material Glass) and PVB (with the defined material PVB).Insert Properties New Structural Properties Create 3D-Property[Right-click on the Properties feature in the Specification Tree New Structural Properties Create 3D-Property]Before the following steps please make sure the Mesh Parts are defined as types:PROPERTY0 – StructuralGlass – StructuralPVB – StructuralThis can be done by going to Tools Set Mesh Parts Type[Right-click on the mesh in the Specification Tree, Set Mesh Part Type Set as Structural Mesh Part]STEP 5In the next step, the model mesh will be imported from two Nastran input files. They each contain a mesh on which we will apply an AML property (Automatically Matched Layer), one on the receiver side, and one on the sender side.:File Import Acoustic Mesh Model Mesh..., and select the file AMLreceiver.bdf Use Meter, Kilogram and Seconds units, and include the materials and properties. Similarly, import AMLsender.bdf.At this point the mesh parts type definition window should look like this:STEP 6Inserting the New Material and properties for the new imported meshesInsert a new Acoustic material as follows (use the default values for air):Insert also a New Fluid Property. Call it also air, use the just defined material 'Air', and apply it to the two Acoustic mesh parts (Sender and Receiver side).STEP 7To facilitate the creation of the structural and acoustic model, some element groups have been predefined in xml files. To import these groups, first create mesh group sets.Insert a New Group Set, either from the contextual menu or with Insert Mesh Grouping Group Set....By right clicking the Group Set feature in the Specification Tree, insert a mesh group named Structural Groups, and in it import the 5 groups from the file StructuralGroups.xml. Right-click the Group Set, and use Mesh Grouping Group Selection Dialog…:Similarly insert a mesh group named Acoustic Groups, and in it import the 4 groups from the file AcousticGroups.xmlRight-click the group set, and use again Mesh Grouping Group Selection Dialog…:Step 8Save the analysis, but without closing.SETTING UP THE ACOUSTIC CASESStep 1Insert a new acoustic automatically matched layer property to take into account thesemi-infinite extent of the sender and receiver rooms. Insert a new AML property byright-clicking Properties, use New Acoustic Properties Automatically Matched Layer Property....Apply it to the two Acoustic groups AML Receiver and AML Sender. Switch the Radiation surface to User Defined, and select the AML Receiver group.Step 2Insert a Direct Vibro-Acoustic Response Analysis Case to compute the structural response and acoustic pressure fields in both the sender and receiver acoustic domains for each of the distributed plane wave excitations:To perform this calculation use No Load function Set and No Load Vector Set.Create new sets for all the rest.STEP 3Expand the Direct Vibro-Acoustic Response Analysis Case from the Specification Tree, right-click the Boundary Condition Set and use Acoustic Sources Distributed Plane Waves... with a Refinement Level of 2, a Radius of4m, and an Acoustic Pressure on 1Pa. The plane waves will be used to excite the system and to calculate the transmission loss characteristics of the panel.Since the panel is not aligned with the xy plane, this coordinate plane cannot be used to define the location of the plane wave sources. So, for the Half Space Plane select Plane defined by Group and select the acoustic group Coupling Sender.Select the Negative Half Space side.Click the OK button to generate a set of 12 spatially distributed plane waves.By now the model should look similar to this:Step 4We will now restrain the border of the glass panel.Right-click the Restraint Set, add an Advanced Restraint on the 3 Translational DOFs, and use as support the Structural Group BCs.Step 5Coupling surface definition will be used to couple the upper and lower surfaces of the panel to the envelope surface of the acoustic cavity. When setting the Coupling Surface, the coupling between the structure and the fluid is on both sides.To correctly define the two-sided coupling in a transmission loss calculation, two coupling surfaces need to be created. From the Coupling Surface Set.1 feature, double-click the Coupling Surface Set.1, and add the two surfaces: Structural Group CouplingSender and Acoustic Group Coupling Sender. Use a tolerance of 10mm and select as Coupling Type One side. Click the Apply button.Do the same for the Receiver Side in the end you should have two Coupling surfaces:Step 6Double-click on the Direct Vibro-Acoustic Response solution to update the analysis parameters. In the current tutorial, the response at the center frequencies of the third octave bands between 160Hz and 2000Hz will be analyzed. In the Result Specifications tab, select User Defined values for the Argument Axis Definition and remove the standard analysis frequency range. Add a new frequency range definition and select a Logarithmic Step definition with a starting frequency of 160Hz, an ending frequency of 2000Hz and a step of 1.122462048. Click the OK button to add the frequency range definition.Request Vector results at Field Points and for the Acoustic Potentials. No need to solve for Structural Displacements for now.Adjust the Solving Parameters. If your system is set up for parallel processing (see the Advanced Acoustic Installation manual), try one of the Parallelism types. Use the Direct solver.Adjust also the Job and Resources, e.g. to use multiple threads.Leave the Output Sets empty, meaning that results will be computed wherever possible.Step 7Update the Direct Vibro-Acoustic Response Solution to compute the acoustic pressure fields and structural deformations. This will take a while, as there are 23 frequencies and 12 load conditions. Save your model.Step 8Displaying the resultsOnce the computation is finished, right-click the Direct Vibro-Acoustic Response Solution Set.1 feature and select Generate Image from the contextual menu.[or select the solution feature and click the Generate Image toolbar button.]The Image Generation dialog box will appear, select the Pressure.Double-click the image feature in the Specification Tree, and in the Occurrences tab select the for example the first Load Condition (meaning the loading by the first distributed plane wave source) and set the frequency at 508Hz, click the OK button. For better visualization you can hide the Nodes and Elements feature, and the Boundary Conditions feature (with its plane wave sources).You can also display the 2D image curve for the Acoustic Power on the Kirchhoff surfaceRight-click the Direct Vibro-Acoustic Response Solution Set.1feature and select New Function Display... from the contextual menu. The New Function Display dialog box will appear requesting you to select the different display images.[Also you can use the button from the toolbar and select the Solution Set feature. A third possibility is to use the menu Insert 2D/3D Images New Function Display]Select the 2D Display from the list and click the Finish button.A new window, containing X- and Y-axes along with the Select Data dialog box will now appear. In the Select Data dialog box, select Kirchhoff Surface Radiation: S and click the Display buttonAs each of the distributed plane wave sources are independent, the sound power can be obtained by simply adding the individual contributions. So, select all 12 Data Cases, and check the option Sum over data cases.Switch the x-axis format to Octaves, and the Y-axis to dB(RMS). You can use dot markers for the curve by right-clicking it, using the Options... command in its context menu, and then changing the settings in the Visualization tab.Save your modelStep 9To get the transmission loss curve, we need to divide the total acoustic power on the receiver side by the total power on the sender side. Before we can do that, we need to combine the individual cases (one for each distributed plane wave source) to get the total power curves.Insert a Random Post-processing Case with Insert Other Analysis Cases Random Post-Processing Case...Refer to the solution of the previous response case, and select to process for a Cross Power Set with Unitary Uncorrelated Load Cases:Update its solution using the context menu on its solution feature Random Response Solution Set.X. This will go fast.Right-click the sub-solution Global Indicator Set.X and create a New Function Display on it. Select the 2D Display as scenario, and click the Finish button.A 2D display window will appear with the Select Data dialog box open. In the General tab, switch the drop-down selector to Transmission Loss, and select the entry Coupled Surface:S and click the Display button.You can see a TL value of 30.461911 dB for the 319.996 Hz octave band:Theory for Panel Transmission LossCalculation of Transmission Loss using Vibro-Acoustic FEMThis topic describes how to set up a model and the computation to compute the Transmission Loss (e.g. for a panel) using the LMS b tools.Step1.Import of an Acoustic and Structural meshImport an acoustic mesh and a structural mesh with the modal data in the Acoustic Harmonic FEM workbench. There is no need to have a field point mesh.Step2. Create a New Acoustic PropertyDefine the Acoustic Properties including fluid properties and possible impedance on the panel. Create an Automatically Matched Layer (AML) property for the source room on all faces that are not coupled to the panel and not touching the joined wall. The wall must be a zero velocity boundary condition. Also create an Automatically Matched Layer (AML) on the anechoic room side, which is defined as a Kirchhoff surface.Step3. Insert the boundary conditionCreate an acoustic boundary condition by selecting Insert Acoustic Boundary Conditions and Sources Acoustic Boundary Condition and Source Set… from the main menu. The Boundary Condition Set Creation dialog box appears as shown in the image below:Click the OK button to close the dialog box. A new Acoustic Boundary Conditions and Sources feature appears in the Specification Tree as shown in the image below:Now, similarly add to the Acoustic Boundary Condition and Sources an acoustic source of type Distributed Plane Waves in the source room.Step4. Insert a Vibro-Acoustic Response and Random Post-Processing Analysis CaseInsert the Modal-based Vibro-Acoustic Response Analysis Case by selecting InsertFEM Analysis Cases Modal Based Vibro-Acoustic Response Analysis Case… from the main menu, or click the Create a Modal Based Vibro-Acoustic Response AnalysisCase… button from the FEM Analysis Cases toolbar. Define the Mesh Mapping and selectthe structural shells and the two groups of acoustic faces (one in the source room and one in the receiver room). Compute the Modal-based Vibro-Acoustic Response Analysis case. It will compute the Incident Power and the Radiated Power for each source.Similarly, insert a Random Post-Processing Case, and Compute it. It will compute the Total Powers and store it in a sub-solution called Global Indicator Set as:∙Total Incident Power, having Physical Type as INPUT_POWER and Response ID asCoupled Surface:S.∙Total Power radiated by the Acoustic Mesh, having Physical Type asACOUSTIC_POWER and Response ID as Kirchhoff Surface Radiation:S.∙If you have a field point mesh which is not needed to compute the Transmission Loss), it will also compute the Total Power on the Field Point Mesh having Physical Type asACOUSTIC_POWER and Response ID as Field Point Mesh:S.The Random Response Solution Set computes also the Transmission Loss with the following formula:Where,is the Incident Poweris the Radiated PowerStep5: Post-ProcessingStandard results will be post-processed on the analysis cases.The Incident Power, Radiated Power and Transmission Loss are stored as Expressions, Load Functions by the Global Indicator Set, and can be displayed in a 2D Function Display.The Transmission Loss will be stored with Physical Type as "ABSORPTIVITY" and Response ID as "Coupled Surface:S"Manual calculation of Transmission Loss by using Edited Load FunctionStep1.Insert an Edited Load Function.To insert an Edited Load Function, select from the main menu Insert Functions CreatorEdited Load Function… or use the Create an Edited Load Function button available in the Functions Creator toolbar.Step2.Import Kirchhoff Surface Radiation:S function from Global Indicators of the Random Post-Processing Solution Set of the Acoustic document. Take only the Real Part.Step3. Again, import the function Acoustic Power on Field Point Mesh:S from Global Indicators of the Random Post-Processing Solution Set of the Structural document. Take only the Real Part and Amplitude of that Part.Step4. Multiply this function with 0.5. As the actual incident power is half the power through the field point mesh. This is because the incident pressure is imposed as total pressure on the wall.Step5. Now, divide these two functions and take the Log of that function and finally multiply it with 10.Step6.Create a 2D displayTo visualize the computed Transmission Loss, right-click the Edited load function in the Specification Tree and select the New Function Display… option from the contextual menu. Select 2D Display from the list and click the Finish button. From the Select Data dialog box select Transmission Loss using the drop-down menu.BEM Symmetry Plane SetThe mathematical formulation of the Boundary Element method leads to dense matrices, with the consequence that a linear increase in model size N (number of nodes and elements, or more generally, number of DOFs) leads toA parabolic increase (order N**2) for the BEM matrix storage requirementsA cubic increase (order N**3) for the BEM matrix solution timeTherefore, it is very advantageous to exploit symmetry characteristics in the geometry of the sound-radiating structure to the full extend. If you need to model only one-half, one-quarter or one-eighth of a vibrating structure, this leads to a drastic reduction in memory requirements and solution time for the problem at hand.The Symmetry Plane Set command allows you to define the acoustical symmetry oranti-symmetry conditions with respect to planes that are parallel to the coordinate axis planes (XY, YZ or XZ). The Symmetry Plane or Baffle will be correctly visualised, if the Mesh is Acoustic (Mesh Type: Acoustic) and a Mesh Preprocessing Set is inserted in the Specification Tree.To insert a new Symmetry Plane Set, click the Insert/Edit a Symmetry Plane Set button in the Acoustic Model Definition toolbar or select Insert Symmetry Plane Set from the main menu. A new dialog box will appear as shown in the image below.Figure: Symmetry and Anti-Symmetry Plane dialogPlanes X, Y and ZThese planes are defined by their position along the perpendicular direction withrespect to the coordinate axis plane; for instance, the X-symmetry plane X=1000mm defines a symmetry plane parallel to the YZ plane and passing through the point(1000,0,0).Although the geometry should always be symmetrical in order to allow the definition of symmetry and anti-symmetry planes, the actual acoustical conditions can besymmetrical (identical) or anti-symmetrical (opposite) with respect to the planedepending on the type of plane selected. The following table summarizes the effect of defining symmetrical or anti-symmetrical conditions for both acoustical and structural boundary conditions:Figure: Symmetry and Anti-Symmetry conditions summaryUp to three mutually perpendicular symmetry or anti-symmetry planes can be defined simultaneously. Of course, only one symmetry or anti-symmetry plane can be defined parallel to each coordinate axis plane XY, YZ or XZ.Since acoustical symmetry implies zero normal velocity, defining a symmetry plane is acoustically equivalent to the presence of a rigid, 100% reflecting floor. In other words, if you are modeling a situation where the sound-radiating structure is located on a hard floor, e.g. the concrete floor of a semi-anechoic chamber, the presence ofthis floor can be represented simply by a symmetry plane.Conversely, since acoustical anti-symmetry implies zero acoustic pressure, defining an anti-symmetry plane is acoustically equivalent to the presence of pressurerelease surface. This kind of surface can be used to model free surfaces like awater-air interface. E.g., if you need to model the acoustic radiation into water from a submarine at a certain depth, you can model the presence of the sea surface above the submarine by defining an anti-symmetry plane.When defining these kinds of planes, they are represented by colored square surfaces. You can also change the colors of the planes by selecting Tools Options AcousticsDisplay tab.∙By default, symmetry planes are represented by semi-transparent bright greensquares with an opaque border as shown in the image below.∙By default, anti-symmetry planes are represented by semi-transparent bright bluesquares with an opaque border as shown in the image below.The presence of these surfaces will also have an important impact on the type of boundary conditions that are created by the Acoustic Mesh Preprocessing operation.BaffleThis functionality is useful for handling the acoustic transparency problems and allows you to compute the insertion or transmission loss. It is only available in the AcousticHarmonic BEM Workbench when the model type is Indirect type. The baffle isrepresented as a symmetry plane but with red color as shown in the image below.The Transmission loss and Insertion loss can be computed in term of pressure or acoustic power. This is quite straightforward when it is done on the pressure, but some postprocessing is needed when it is done on the power. The Incident Power and Transmitted Power can be calculated by using the following formulae.Incident PowerUsually for the transmission loss computation, an acoustic diffuse field is defined on one side of the baffle. The Incident Power can be computed with the following formula:where Prms is the diffuse field acoustic RMS pressure and S is the surface of the structure impacted by the incident diffuse field. This is valid for a diffuse field generated by a sum of plane waves. The total input power is the sum of the individual source power. This can be easily computed in an edited load function.Transmitted PowerThe Transmitted Power can be computed by defining a hemispherical field point mesh almost touching the baffle and computing the field response. The total Transmitted Power will then be computed in the random post processing case. When updating the solution, if there is acoustic power through field point mesh available in the input solution, the total acoustic power will be computed with the following equation:where Wt is the total acoustic power, NLC is the number of pseudo load-cases, are the singular values (Virtual Autopowers) and Wi is the acoustic power for load case i.。
基于Virtual Lab／Acoustic的发动机结构噪声预测
本 文建 立 了发 动机 主 要 部件 的有 限元 模 型 ， 进 行 了动力 学分 析 ， 加 发动 机 的主 要激 励 后 ， 施 用
ＭＳ ／ Ａ Ｔ Ａ Ｃ Ｎ Ｓ Ｒ Ｎ计 算发 动机 的振 动 响应 ， 后 采 用 最
进行 发动 机结 构 噪 声 预测 ， 要 进行 大量 的研 需 究工作 。图 １为发 动机结 构 噪声 预测 的基本 流程 。
维普资讯
２０ ０７年 １ ２月
噪声Biblioteka 与振动控
制
第 ６期
文章编号 ：０６— ３ ５ ２ ０ ）６— ０ ０— ４ １０ １５ （ ０ ７ ０ ０ ８ ０
基 于 Ｖ ｒｕ ｌ ａ ／ ｏ ｓ ｃ的 发 动机 结 构 噪 声 预 测 ｉ ａ ｂ Ａｃ ｕｔ ｔ Ｌ ｉ
ａ ｄ ｓ ｕ ｔ ｒ ｌ ｉ ｒ ｔ ｎ ｒ ｓ ｏ ｓ ａ ｃ ｌ ｔ ｎ，ｓ ｕ ｔｒ ｌａ ｏ ｓ ｃ ｐ ｅ ｉ ｔ ｎ ｈ ｓｂ ｅ ｍｐ ｅ ｎ ｅ ｙ Ｌ ｎ ｔ ｃｕ ａ ｖ ｂ ａ ｉ ｅ ｐ ｎ ｅ ｃ ｌｕ ａｉ ｒ ｏ ｏ ｔ ｃｕ ａ ｃ ｕ ｔ ｒ ｄ ｃｉ ａ ｅ ｎ ｉ ｌ ｍｅ ｔ ｄ ｂ ＭＳ ｒ ｉ ｏ
ａ ｃ ｓ ｔ ｒ ｄｉｔｎ ｉｅ ｉ ｅ ｉｎ ｐ ｒｏ ｎ ｏ ｍｉ ｍｉｅ ｔ ａ ｉ ｔｄ ｎ ｉｅ．Ａｆｅ ｈ ｙ ｍｉ ｎ ｌ ｓｓ ｎ ｅ ｉ ｏ ｐ ｅ ｃ ｏｓ ｎ ｄ ｓｇ ｏ ｄ ａ ｄ ｔ ｎｉ ｚ ｈｅ ｒ ｄ ａｅ ｏ ｓ ｉ ｔ ｒ ｔ ｅ ｄ ｎａ ｃ ａ ａｙ ｉ
Ｓ ｒ ｃ ｕｒ ｌＮｏ ｓ ｅ ｉｔｏ ｆＥｎｇｎｅ Ｂａ ｅ ｎ ｒｕａＬａ Ａｃ ｕ ｔｃ ｔ ｕ ｔ ａ ｉｅ Ｐｒ ｄ ｃｉ ｎ ｏ ｉ ｓ ｄ ｏ Ｖｉｔ ｌ ｂ／ ｏ ｓｉ
基于Virtual.Lab的永磁同步电机噪声仿真
3 电磁仿真及电磁力分析
3.2 电磁力分析出，并导入LMS b。再通 过定子内表面将电磁力映射到结构有限元模型上，如左下图所示。将时域内的电磁力信号转化为频域信号， 并作出colormap图，如右下图所示。可以看到电磁力以第8阶、第16阶、第24阶、第32阶为主。
电机辐射噪声的阶次成分主要由电磁力产生，结构本身的影响主要体现在共振带上。对于共振问题， 可以利用LMS b的贡献量分析技术，识别原因。
针对8000rpm、4839Hz的声压响应峰值，计算针对该点的面板贡献度，面板分块如左下图所示， 面板贡献度如右下图所示。4839Hz处主要贡献区域为前盖板。类似分析可为结构优化提供方向。
驱动电机的振动噪声主要由电磁力激振产生。我们 当然希望在电机设计阶段就能预测其振动噪声特性。但 之前我们在开发中，仅能根据经验去设计电机，或者参 考一些经典书籍
进行工程估算，计算复杂且精度很难控制。 本文利用LMS b的振动噪声模块，快速预测电机的电磁振动噪声，为电磁设计及结构
设计提供了一定的指导方向。
order:8
order:32 order:24
order:16
FDM
4 辐射噪声计算及分析
利用模态叠加法求解出各个转速下10010000Hz的振动响应，输出结构表面的振动位 移。然后开始使用LMS b声学模块的 有限元法，求解电机的辐射噪声。
声学有限元模型如右图所示。 由于设计时需要反复计算多个转速工况的响 应，为了加快计算速度，这里采用基于声学传递 向量（ATV）的计算方法。
在材料库中选取各部件对应的弹性模量、泊松比、密度等参 数。
FDM
2.2 模态分析结果
2 电机有限元模型及模态分析
直接在LMS b中进行自由模态分析，主要阶次见下图：
基于Virtual Lab的汽车消声器声学性能优化
基于Virtual Lab的汽车消声器声学性能优化摘要：探讨采用声学有限元软件virtual lab分析消声器声学性能的方法，对市面上的一款内部结构复杂的汽车消声器的插入损失和传递损失进行分析，采用对消声器隔板增加穿孔板结构的方法对原消声器进行了改进，尝试对其声学性能进行优化，优化结果表明了改进措施的有效性。
abstract: in this paper, the method is presented to analyzethe acoustical performance of a muffler with complicatedchambers on the market by using the acoustic fem softwarevirtual lab. insert loss and transmission loss of the mufflerare calculated, and the original acoustical performance isimproved through adding additional perforated structure. the comparison of the insert loss and transmission loss of themodified and original mufflers demonstrates theeffectiveness of the optimization scheme.关键词：有限元；声学分析；消声器；传递损失key words: fem；acoustics analysis；muffler；transmissionloss中图分类号：u46 文献标识码：a 文章编号：1006-4311（2012）11-0045-020 引言消声器的声波符合平面波的规律，早从1950年代开始其相关的理论研究。
virtuallab
产品简介LMS b Motion多体动力学LMS b Motion多体动力学能够让设计师和工程师真实地仿真整车设计中驾驶的平顺性及操纵的稳定性，新型挖掘机的运转，或者机械开关的可靠性等。
LMS b Motion多体动力学作为先进的MBS解决方案，结合了具有自动化程序的集成仿真环境和广泛的应用领域，包括动力总成动力学、悬架动力学、履带动力学等。
此外，仿真结果还可以用于后续的与耐久性或者噪声振动分析相关的研究，例如高精度求解器预测的覆盖整个频率范围的动态内部载荷。
∙LMS b Standard Motion 标准动力学软件LMS b Standard Motion是一个对机械系统真实运动和载荷进行仿真的完整集成解决方案。
它能使工程师在进行昂贵的实物样机试验前快速地分析和优化机械设计的真实性能，并能保证机构具有预期功能。
LMS b Standard Motion使用户能够建立和模拟多刚体机械系统，改进它们的动力学性能，预测部件和系统的载荷，以便用于结构分析、振动噪声模拟、疲劳寿命预测和其它分析。
LMS b Standard Motion在实体建模、参数化、CAD几何体、柔性体特点、控制和液压功能、求解器性能、动画显示和后处理功能等方面提供了极具前沿的领先技术。
它独创地把所有需要的功能集成到一个用户界面友好的桌面环境，不需要其它求解器，并消除了费时的数据转换。
采用LMS b Standard Motion，用户可以利用一个基于CATIA V5的完全集成的CAD引擎，快速地创建和改进他们的机械系统的虚拟样机模型。
实体建模器可以得到一个完整的参数化模型。
机械单元包括弹簧、摩擦力、接触力和广泛的运动副和约束功能。
稳定和高性能的求解器对即使是最复杂的动力学问题都能保证精确和高效的处理。
数据结果中包括位移、速度、加速度和模型所有部件的相互作用力。
专门的动画显示和后处理特点可以帮助工程师轻松地识别并有效地解决某个工程问题的根本原因。
基于LMS Virtual Lab Acoustics的发动机结构噪声预测
基于LMS VirtualLab Acoustics的发动机结构噪声预测作者：邓晓龙李修蓬奇瑞汽车工程研究院动力总成开发部邓晓龙李修蓬摘要：在发动机设计阶段就进行发动机结构噪声预测，并在此基础上进行噪声最优化控制，是提升发动机的NVH性能的根本手段。
在对发动机进行动力学分析、结构响应振动计算后，采用LMS Virtual Lab/Acoustic软件进行了发动机结构噪声预测。
关键词：发动机; 噪声预测;1 前言随着我国汽车自主创新的不断深入，从设计阶段开始就同步进行计算机仿真成为发动机开发的基本需求。
CAE技术的大量应用，降低了发动机开发的成本，缩短了开发周期，提升了产品性能。
汽车的NVH（Noise,Vibration and Harshness；噪声、振动与舒适性）性能日益受到重视，发动机是汽车最主要的振动及噪声源，在发动机的设计阶段就深入进行振动噪声性能的预测与优化，是发动机自主研发过程中非常重要的一项工作。
国内外研究人员对发动机结构噪声的预测做了大量的研究工作，中低频的结构噪声预测方法已经趋于成熟。
出现了一些可进行噪声预测的商业软件，如LMS公司的Virtual Lab/Acoustic 等。
结构振动响应与辐射噪声之间的关系非常复杂，目前根据强迫振动响应计算辐射噪声的计算方法主要有平板理想化法、有限元法和边界元法等[1]。
噪声预测技术的发展，使得发动机在设计阶段进行噪声评价成为可能。
本文建立了发动机主要部件的有限元模型，通过AVL/EXCITE软件，进行了动力学分析，施加发动机的主要激励后，用MSC/NASTRAN计算发动机的振动响应，最后采用Virtual Lab/Acoustic进行噪声预测。
2 结构噪声预测理论2.1 发动机结构噪声预测流程进行发动机结构噪声预测，需要进行大量的研究工作。
图1为发动机结构噪声预测的基本流程。
图1 发动机辐射噪声预测流程2.2 发动机结构强迫振动响应在计算强迫振动响应时，假设发动机受到随时间变化的激励力的作用，系统为线弹性振动。
声疲劳仿真计算实例-virtual.lab版
Step 4 Carry out the acoustic preprocessing
Insert->Acoustic mesh preprocessing set.
Double click the Grid Support in the tree and the select the acoustic mesh. Right click on the Acoustic Mesh Preprocessing Set and select Update.
声疲劳仿真计算实例
Acoustic fatigue
By Li Zenggang
Mobile: Email: forengineer@
Step 1 Import the structure and acoustics meshes
Start->Acoustics->Acoustic Harmonic BEM File->Import. First select nastran input file
Step 5 Define the material and property
Insert-> Materials->New Materials ->New fluid
Material. Accept the default value. Change the Name to air. Insert ->Properties->New Properties -> New acoustic fluid property. Select the acoustic mesh and the fluid material from tree.
计算发动机辐射噪声详细步骤（Virtual.lab版）
计算发动机辐射噪声详细步骤（b版）用直接边界元法计算发动机辐射噪声详细步骤（b版）(******************************@)（from 《b Acoustics声学仿真计算高级应用实例》）本例也可以用sysnoise来实现（1）进入声学边界元环境启动b后，单击菜单【Start】→【Acoustics】→【Acoustic Harmonic BEM】进入声学边界元环境，如图4-1所示。
图4-1 进入声学边界元（2）设定分析模型的类型本例由于是计算发动机壳的辐射声场，这个声场是发动机的外声场，因此选用直接边界元外声场即可。
单击菜单【Tools】→【Edit the Modal Type Definition】，弹出分析模型参数对话框，如图4-2所示，选择Direct Exterior Element，单击【OK】按钮关闭对话框。
图4-2 设定边界元类型的对话框（3）导入发动机结构网格单击菜单【File】→【Import】，然后将文件格式Files of type 设置为NASTRAN Bulk File，然后选择本书附带光盘Chaptor_04\Engine目录下的Engine_Structure.bdf文件，单击【Open】按钮，然后弹出导入对话框，只选择Finite Element Mesh 项，并将长度单位设置成Meter，质量单位设置成Kilogram，时间单位设置成Second，单击【OK】按钮可以导入发动机的网格。
（4）导入发动机的振动加速度单击菜单【Insert】→【Vector & Function Sets】→【Load Vector Set】，弹出定义Vector 的对话框，如图4-3（a）所示，在Name输入框中输入Engine Acceleration Set，Physical Type 设置成Accelerations，Data Class设置成Frequency Spectra，单击【OK】按钮关闭对话框。
多孔吸声型声屏障降噪效果仿真分析
多孔吸声型声屏障降噪效果仿真分析作者：刘冬楚珑晟张明杰陈翊民来源：《计算机辅助工程》2017年第04期摘要：利用边界元法建立高速铁路区间直立型声屏障降噪预测模型，对添加硅酸盐基多孔吸声材料前后声屏障对降噪效果的影响进行数值计算。
结果表明：厚度为0.08 m的硅酸盐基多孔吸声材料使得声屏障在距离线路中心30 m的铁路界限处噪声衰减量最大可增加12.5 dB；应用于声屏障的最佳硅酸盐基多孔吸声材料厚度为0.08～0.11 m。
关键词：声屏障；高速铁路；硅酸盐基多孔吸声材料；声压级；边界元中图分类号：U238；TU112.594 文献标志码：B0引言交通运输的快速发展，大大方便人们出行，促进物资的流通，在实现资源优化配置方面起到巨大的作用。
然而，高速铁路的快速发展在给人们的出行带来方便、快捷和舒适的同时，其噪声也给周边环境带来一定的影响。
采用声屏障是降低铁路对周边环境噪声污染的有效途径。
英国、法国等欧洲国家在建设高速铁路时大量采用声屏障来降低噪声对周边环境的影响；日本在建立新干线时，为避免扰民于线路重要区段设置大量声屏障。
铁路声屏障按降噪机理不同分为隔声声屏障和吸声声屏障2种。
我国高速铁路设置的声屏障主要是隔声声屏障，通过设计不同的结构形式有效降噪，但隔声声屏障只改变噪声的传播，并不消耗声能。
在声屏障一侧添加多孔吸声材料，利用吸声材料的吸声特性可在原声屏障的基础上增加降噪效果，然而其如何影响声屏障的降噪效果尚未见报道。
由于影响声屏障降噪效果的因素很多，而研究各种因素对降噪效果影响的方法却有一定局限性，如何从中选择经济实用的方案，至今依然没有成熟的理论来指导，目前采用最多的是利用计算机模拟技术对该类问题进行研究。
国外学者大量应用计算机技术对声屏障的降噪效果进行数值模拟，可大大提高准确性和效率。
近年来，我国研究人员也开始重视应用计算机仿真模拟技术对声屏障的降噪效果进行预测，为设计高效的声屏障提供参考依据。
Virtual.lab声固耦合的隔声量仿真分析教程
FEM Direct Vibro-Acoustic Analysis Case TutorialObjective:The goal of this tutorial is to calculate the acoustic response of a glass/PVB plate (a laminated safety glass with a Polyvinyl butyral layer in between)・The tutorial includes using the following analysis cases:•Structural Modal case•Direct Structural Forced Response•Direct Structural Vibro-Acoustic Response•Transmission LossThe model contains a Visco-elastic frequency-dependent material・Pre-Requisites:Software Configurations that are needed to run the tutorial:•Licenses to set up the case in LMS b:u Desktop (VL-HEV.21.1 or equivalent)1' and "FiniteElement Acoustics (VL-"•When solving the acoustic response case, the license for product U LMS b FEM Vibro-Acoustics Structural Solver VL-VAM.45.2” is needed・•Solving the Random Post-processing case to get the T「ansmission Loss curve will require the license for n Random Vibro Acoustic Analysis (VL-nTutorial Data Files:StructuralGroups ・ xmlSAFyoung ・ xlsLaminatedStructure ・bdfFPmesh ・bdfAMLsender ・ bdfAMLreceiver ・bdfAcousticGroups ・ xml[All data files can be found on the APPS n DOCS DVD, in an archive called VAM_DirectVA-TL. For ease of use, it is best to copy all files to a local folder.]STEP BY STEP Tutorial:STEP 1After starting LMS b, create a new document in the Acoustic Harmonic FEMWorkbench (Start -^Acoustics -^Acoustic Harmonic FEM).STEP 2Select File -^Import from the main menu ・[The Import comma nd can also be selected from the con textualmenu of the Links Man ager, by right clicking]A file selector window appears allowing you to specify the file type and the file name・[For more details, see ]Select the file type NASTRAN Bulk File (匸bdf, *・NS# ^.nas f \dat) and browse for the file Laminatedstructure ・bdf and click the Open butt on. A new dialog box appears requesting the selection of data that needs to be imported from the file. The data entries that are not available in the file are grayed out. Select in Split into Multiple Mesh Pa「tsun der Mesh Creation and set the unit system to Meter, Kilogram, Second, click the OK buttOn.STEP 3Next, the d iff ere nt structural materials will be defined ・ The two outer layers of the panel are made of Glass ・To in corporate the 2% structural dampi ng of this material, it will be modeled as a viscoelastic material with a constant complex You ng modulus ・ The inner layer is made of PVB.Insert -^Materials -^New Materials -^New Viscoelastic Material...[Right-click on the Materials feature in the Specification Tree -^New Materials -^New Viscoelastic Material] Define the materials as follows:The PVB material at the center of the windshield has strong frequency dependent stiffness properties and is n early in compressible ・ The frequency depe ndency can be in corporated in a viscoelastic material using an edited load function. The values can be imported from the Excel document SAFyoung.xls as follows:Check Frequency Dependent, and right-click the input field・Select New Function・In the Attributes tab, enter as Name Young" s modulus PVB・In the Values tab, click the Import a file button, and browse to the excel file to select it.Switch the Data Format to Linear AmpHtude/Phase (deg) because the file contains the values like that. Click the Import butt on.Click the OK button of the Function Editor GULClick the OK button on the Material GULOn the Edited Load Function Set, create (usi ng the con text menu) a 2D display & type Comp/ex (Edited Load Function) on the Young's modulus and check the curve:STEP 4Defining two Structural 3D properties for Glass and PVB, applied to the structural groups Glass (with the defined material Glass) and PVB (with the defined material PVB).Insert -^Properties -^New Structural Properties -^Create 3D-Property[Right-click on the Properties feature in the Specification Tree-^- New Structural Properties -^•Create 3D-Property]Before the following steps please make sure the Mesh Parts are defined as types:PROPERTY0 一StructuralGlass 一StructuralPVB 一StructuralThis can be done by going to Tools -^Set Mesh Parts Type[Right-click on the mesh in the Specification Tree, Set Mesh Part Type -^Set as Structural Mesh Part]STEP 5In the next step, the model mesh will be imported from two Nastra n in put files ・ They each contain a mesh on which we will apply an AML property (Automatically Matched Layer), one on the receiver side, and one on the sender side.:File -^Import Acoustic Mesh -^Model Mesh..., and select the file AMLreceiver .bdfUse Meter, Kilogram and Seconds un its, and in elude the materials and properties ・Similarly, import AMLsender ・bdf ・At this point the mesh parts type definition window should look like this:STEP 6Inserting the New Material and properties for the new imported meshesInsert a new Acoustic material as follows (use the default values for air):Insert also a New Fluid Propert y. Call it also air, use the just defined material 'Air', and apply it to the two Acoustic mesh parts (Sender and Receiver side).STEP 7To facilitate the creation of the structural and acoustic model, some element groups have been predefined in xml files・ To import these groups, first create mesh group sets・Insert a New Group Set, either from the contextual menu or with Insert -^Mesh Grouping -^•Group Set....By right clicking the Group Set feature in the Specification Tree, insert a mesh group named Structural Groups, and in it import the 5 groups from the file structuralGroups ・ xml ・Right-click the Group Set, and use Mesh Grouping -^Group Selection Dialog...:Similarly insert a mesh group named Acoustic Groups, and in it import the 4 groups from the file AcousticGroups ・ xmlRight-click the group set, and use again Mesh Grouping ->Group Selection Dialog...:Step 8Save the analysis, but without closing.SETTING UP THE ACOUSTIC CASESStep 1Insert a new acoustic automatically matched layer property to take into account the semi-infinite extent of the sender and receiver rooms・ Insert a new AML property by right-clicking Properties, use New Acoustic Properties -^Automatically Matched Layer Property....Apply it to the two Acoustic groups AML Receiver and AML Sender. Switch the Radiation surface to User Defined, and select the AML Receiver group・Step 2Insert a Direct Vibro・Acoustic Response Analysis Case to compute the structural response and acoustic pressure fields in both the sender and receiver acoustic domains for each of the distributed plane wave excitations:To perform this calculation use No Load function Set and No Load Vector Set.Create new sets for all the rest.STEP 3Expand the Direct Vibro・Acoustic Response Analysis Case from the Specification Tree, right-click theBoundary Condition Set and use Acoustic Sources -^Distributed Plane Waves... with a Refinement Leveled 2, a Radius & 4m, and an Acoustic Pressure on lPa. The plane waves will be used to excite the system and to calculate the transmission loss characteristics of the panel.Since the panel is not aligned with the xy plane, this coordinate plane cannot be used to define the location of the plane wave sources・ So, for the Half Space Plane select Plane defined by Groups nd select the acoustic group coupling sender ・Select the Negative Half Space side.Click the OK butt on to gen erate a set of 12 spatially distributed plane waves ・By now the model should look similar to this:Step 4We will now restrain the border of the glass panel.Right-click the Restraint Set, add an Advanced Restraint QV\ the 3 Translational DOFs, and use as support the Structural Group BCs.Step 5Coupling surface definition will be used to couple the upper and lower surfaces of the panel to the envelope surface of the acoustic cavity・ When setting the Coupling Surface, the coupling between the structure and the fluid is on both sides.To correctly define the two-sided coupling in a transmission loss calculation, two coupling surfaces need to be created・ From the Coupling Surface Set.1 feature, double-click the Coupling Surface Set.1, and add the two surfaces: Structural Group CouplingSender and Acoustic Group Coupling Sender. Use a toleranee of 10mm and select as Coupling Type One side. Click the Apply button.Do the same for the Receiver Side in the end you should have two Coupling surfaces:Step 6Double-click on the Direct Vibro-Acoustic Response solution to update the analysis parameters. In the current tutorial, the response at the center frequencies of the third octave bands between 160Hz and 2000Hz will be analyzed・ In the Result Specifications tab, select User Defined for the Argument Axis Defin ition and remove the stan da rd an alysis freque ncy range・ Add a new frequency「ange definition and select a Logarithmic Step definition with a starting frequency of 160Hz, an ending frequency of 2000Hz and a step of 1 ・ 8. Click the OK butt on to add the frequency「ange defi nition.Request lector results at Field Points and for the Acoustic Potentials. No need to solve for Structural Displacements for now・Adjust the Solving Parameters・If your system is set up for parallel processing (see the Advaneed Acoustic Installation manual), try one of the Parallelism types・ Use the Direct solver.Adjust also the Job and Resources, e.g. to use multiple threads・Leave the Output Sets empty, meaning that results will be computed wherever possible.Step 7Update the Direct Vibro-Acoustic Response Solution to compute the acoustic pressure fields and structural deformations. This will take a while, as there are 23 frequencies and 12 load conditions. Save your model.Step 8Displaying the resultsOnce the computation is finished, right-click the Direct Vibro-Acoustic Response Solution Set.l feature and select Generate Image from the con textual menu ・[or select the solution feature and click the Gen erate Image toolbar butt on.]The Image Generation dialog box will appear, select the Pressure.Double-click the image feature in the Specification Tree, and in the Occurrences tab select the for example thefirst Load Condition (meaning the loading by the first distributed plane wave source) and set the freque ncy at 508Hz, click the OK butt on. For b etter visualizati on you can hide the Nodes and Elements feature, and the Boundary Conditions feature (with its plane wave sources)・You can also display the 2D image curve for the Acoustic Power on the Kirchhoff surfaceRight-click the Direct Vibro-Acoustic Response Solution Set.1 feature and select New Function Display..・from the con textual menu. The New Function Display dialog box will appear requesting you to select the different display images・[Also you can use the 匸button from the toolbar and select the Solution Set feature. A third possibility is to use the menu Insert ->2D/3D Images ->New Function Display] Select the 2D Display from the list and click the Finish button.A new window, containing X- and Y-axes along with the Select Data dialog box will now appear. In the Select Data dialog box, select Kirchhoff Surface Radiation: Sand click the Display button As each of the distributed plane wave sources are independent, the sound power can be obtained by simply adding the individual contributions・ So, select all 12 Data cases, and check the option Sum over data cases・Switch the x-axis format to Octaves, and the Y-axis to dB(RMS). You can use dot markers for the curve by right-clicki ng it, using the Opti ons …command in its con text menu, and the n changing the settings in the Visualization tab・Save your modelStep 9To get the transmission loss curve, we need to divide the total acoustic power on the receiver side by the total power on the sender side. Before we can do that, we need to combine the individual cases (one for each distributed plane wave source) to get the total power curves・Insert a Random Post-processing Case with Insert ->Other Analysis Cases -^-Random Post-Processing Case...Refer to the solution of the previous response case, and select to process for a Cross Power Set with Unitary Uncorrelated Load Cases:Update its solution using the context menu on its solution feature Random Response Solution Set.X. This will go fast.Right-click the sub-solution Global Indicator Set.X and create a New Function Display QV\ it. Select the 2D Display as seenario, and click the Finish button.A 2D display window will appear with the Select Data dialog box open. In the General tab, switch the drop-down selector to Transmission Loss, and select the entry Coupled Surfaced and click the Display button.You can see a TL value of 30.461911 dB for the 319.996 Hz octave band:Theory for Panel Transmission LossCalculation of Transmission Loss using Vibro-Acoustic FEMThis topic describes how to set up a model and the computation to compute the Transmission Loss (e.g・ for a panel) using the LMS b tools・Stepl ・Import of an Acoustic and Structural meshand a structural mesh with the modal data in the Acoustic Harmonic FEM workbench・ There is no need to have a field point mesh.Step2. Create a New Acoustic PropertyDefine the Acoustic Properties jn eluding fluid properties a nd possible impedance g the panel. Create an property for the source room on all faces that are not coupled to the panel and not touching the joined wall. The wall must be a zero velocity boundary condition. Also create an Automatically Matched Layer (AML) on the an echoic room side, which is defi ned as a Kirchhoff surface ・Step3. Insert the boundary conditionCreate an acoustic boundary condition by selecting Insert -^Acoustic Boundary Conditions and Sources -^Acoustic Boundary Condition and Source Set... from the main menu. The Boundary Condition Set Creation dialog box appears as shown in the image below:Click the OK button to close the dialog box. A new Acoustic Boundary Conditions and Sources feature appears in the Specification Tree as shown in the image below:Now, similarly add to the Acoustic Boundary Condition and Sources an acoustic source of type in the source 「oom.Step4. Insert a Vibro-Acoustic Response and Random Post-Processing Analysis CaseInsert the Modal-based by selecting Insert -^FEM Analysis Cases -^Modal Based Vibro -Acoustic Response Analysis Case..・from the main menu, or click the Create a Modal Based Vibro-Acoustic Response Analysis Case...麹butto n from the FEM Analysis Cases toolbar. Define the Mesh Mapping and select the structural shells and the two groups of acoustic faces (one in the source room and one in the receiver room). Compute the Modal-based Vibro-Acoustic Response Analysis case・ It will compute the Incident Power and the Radiated Power for each source・Similarly, insert a z and Compute it. It will compute the Total Powers a nd store it in a sub-solution called Global Indicator Set as:•Total Incident Power, having Physical Type as INPUT^POWER and Response ID as Coupled Surfaced.•Total Power radiated by the Acoustic Mesh, having Physical Type as ACOUSTIC_POWER andResponse ID as Kirchhoff Surface Radiation:S.• If you have a field point mesh which is not needed to compute the Transmission Loss), it will alsocompute the Total Power on the Field Point Mesh having Physical Type as ACOU5TIC_POWER andResponse ID as Field Point Mesh:S.The Random Response Solution ^computes also the Transmission £055 with the following formula:Where,is the Incident Power^out is the Radiated PowerSt 即5: Post-ProcessingStandard results will be post-processed on the analysis cases.The Incident Power, Radiated Power a nd Transmission Loss are stored as Expressions, Load Functions by the Global Indicator Set, and can be displayed in a 2D Function Display.The Transmission Loss will be stored with Physical Type as "ABSORPTIVITY"and Response ID as "Coupled Surface:S,rManual calculation of Transmission Loss by using Edited Load FunctionStepl. Insert an ・To insert an Edited Load Function, select from the main menu Insert -^Functions Creator ■^■Edited Load Function... or use the Create an Edited Load Function ^^button available in the Functions Creator toolbar・Step2. Import Kirchhoff Surface Radiation :S fu nction from Global Indicators of the Random Post-Processing Solution Set of the Acoustic document. Take only the Rea/Part.Step3. Again, import the function Acoustic Power on Field Point Mesh:S from Global Indicators of the Random Post-Processing Solution Set of the Structural document. Take only the Real Part and Amplitude of that Part. Step4. Multiply this function with 0.5. As the actual incident power is half the power through the field point mesh. This is because the in cident pressure is imposed as total pressure on the wall.Step5 ・Now, divide these two fun ctions and take the Log of that function and fin ally multiply it with 10.Step6.To visualize the computed Transmission Loss, right-click the Edited load function in the Specification Tree and select the New Function Display..・opti on from the con textual menu ・ Select 2D Display from the list and click the Finish button. From the Select Data dialog box select Transmission Loss using the drop-down menu. BEM Symmetry Plane SetThe mathematical formulation of the Boundary Element method leads to dense matrices, with the con sequence that a lin ear increase in model size N (number of nodes and elements, or more gen erally, nu mber of DOFs) leads toA parabolic increase (order N**2) for the BEM matrix storage requirementsA cubic increase (order N**3) for the BEM matrix solution timeTherefore, it is very advantageous to exploit symmetry characteristics in the geometry of the sound-radiating structure to the full extend. If you need to model only one-half, one-quarter or one-eighth of a vibrating structure, this leads to a drastic reduction in memory requirements and solution time for the problem at hand・The Symmetry Plane Set comma nd allows you to defi ne the acoustical symmetry or anti-symmetry conditionswith respect to planes that are parallel to the coordinate axis planes (XY, YZ or XZ). The Symmetry Plane or Baffle will be correctly visualised, if the Mesh is Acoustic (Mesh Type: Acoustic) and a Mesh Preprocessing Set is inserted in the Specification Tree・To insert a new Symmetry Plane Set, click the Insert/Edit a Symmetry Plane Set button in the Acoustic Model Definition toolbar or select Insert -^Symmetry Plane Set from the main menu. A new dialog box will appear as shown in the image below・Figure: Symmetry and Anti-Symmetry Plane dialog• Planes X, Y and ZThese planes are defi ned by their position along the perpe ndicular di recti on with respect to thecoordinate axis plane; for instan ce, the X-symmetry plane X=1000mm defines a symmetry plane parallel to the YZ plane and passing through the point (1000,0,0)・Although the geometry should always be symmetrical in order to allow the definition of symmetry andanti-symmetry planes, the actual acoustical conditions can be symmetrical (identical) or anti-symmetrical (opposite) with respect to the plane depending on the type of plane selected・ The following tablesummarizes the effect of defining symmetrical or anti-symmetrical conditions for both acoustical andstructural boundary conditions:Figure: Symmetry and Anti-Symmetry conditions summaryUp to three mutually perpendicular symmetry or anti-symmetry planes can be defined simultaneous!y.Of course, only one symmetry or anti-symmetry plane can be defined parallel to each coordinate axisplane XY, YZ or XZ・Since acoustical symmetry implies zero normal velocity, defining a symmetry plane is acousticallyequivalent to the presence of a rigid, 100% reflecting floor・In other words, if you are modeling a situation where the sound-radiating structure is located on a hard floor, e.g. the concrete floor of asemi-anechoic chamber, the presence of this floor can be represented simply by a symmetry plane.Conversely, since acoustical anti-symmetry implies zero acoustic pressure, defining an anti-symmetryplane is acoustically equivalent to the presence of pressure release surface・This kind of surface can be used to model free surfaces like a water-air interface. E.g., if you need to model the acousticradiati on into water from a submarine at a certain depth, you can model the presence of the seasurface above the submarine by defining an anti-symmetry plane.When defining these kinds of planes, they are represented by colored square surfaces. You can also change the colors of the planes by selecting Tools -^Options AcousticsDisplay tab.•By default, symmetry planes are represented by semi-transparent bright green squares with anopaque border as shown in the image below・•By default, anti-symmetry planes are represented by semi-transparent bright blue squares with anopaque border as shown in the image below・The presenee of these surfaces will also have an important impact on the type of boundary conditions that are created by the Acoustic Mesh Preprocessing operation.•BaffleThis functionality is useful for handling the acoustic transparency problems and allows you to computethe insertion or transmission loss. It is only available in the Acoustic Harmonic BEM Workbench when the model type is Indirect type. The baffle is represented as a symmetry plane but with red color as shown in the image below・The Transmission loss and Insertion loss can be computed in term of pressure or acoustic power. This is quite straightforward when it is done on the pressure, but some postprocessing is needed when it is done on the power・ The Incident Power and Transmitted Power can be calculated by using the following formulae・Incident PowerUsually for the transmission loss computation, an acoustic diffuse field is defined on one side of the baffle・ The Incident Power can be computed with the following formula:where Prms is the diffuse field acoustic RMS pressure and S is the surface of the structure impacted by the incident diffuse field・ This is valid for a diffuse field generated by a sum of plane waves ・ The total in put power is the sum of the individual source power. This can be easily computed in an edited load function・Transmitted PowerThe Transmitted Power can be computed by defining a hemispherical field point mesh almost touching the baffle and computing the field response. The total Transmitted Power will then be computed in the「andom post processing case・ When updating the solution, if there is acoustic power through field point mesh available in the in put solutio n, the total acoustic power will be computed with the following equation:where Wt is the total acoustic power, NLC is the number of pseudo load-cases, 5 are the singular values (Virtual Autopowers) and Wi is the acoustic power for load case i.。
基于Virtual Lab研究影响空气滤芯消声能力的因素
10.16638/ki.1671-7988.2020.18.044基于Virtual Lab研究影响空气滤芯消声能力的因素李光武，王志强（华晨汽车工程研究院动力总成综合技术处，辽宁沈阳110000）摘要：进气系统噪声是汽车的主要噪声源之一，它直接影响着车内噪声和通过噪声，从而影响着驾乘人员的驾乘感受和能否满足通过噪声的法规要求。
空气滤清器作为进气系统的关键零部件之一，它不仅仅起到保护发动机的能力，还具备着降低进气系统噪声的能力。
空气滤芯作为多孔介质，不仅能吸收噪声，还可以通过多孔区域将声能转化为热能从而消除噪声，而影响空气滤芯降噪能力的因素主要为流阻率、孔隙率和结构因子，而三个因素是如何影响空气滤芯的消音能力就需要通过仿真分析进行验证。
文章通过Hyper mesh和Virtual Lab软件进行传递损失联合仿真分析，验证各个因素对滤芯消声能力的影响。
关键词：空气滤芯；Hyper mesh；Virtual Lab；传递损失中图分类号：U467.4 文献标识码：A 文章编号：1671-7988(2020)18-131-03Using Virtual Lab to Valid Factors Effect Ability of Noise Eliminationof Air Filter ElementLi Guangwu, Wang Zhiqiang( Brilliance Auto R&D Center, Powertrain Integrated Technology Section, Liaoning Shenyang 110000 )Abstract: Noise of intake system is one of the main noise souse of vehicle, it affects noise level of driving cab and bass-by noise directly, thus driving feeling and regulation of bass-by noise will be affected. As a main component of vehicle, air filter box not just protects engine, also has ability of noise elimination. As a porous material, air filter element can absorb noise, also can transfer acoustic power to heating power and eliminate noise. There are three factors influence ability of noise elimination of air filter element, they are flow resistivity, porosity and tortuosity, we need to valid how the factors impact ability of noise elimination by simulation. Hyper mesh and Virtual Lab will be used to simulate transmission loss of air filter box and valid factors effect ability of noise elimination.Keywords: Air filter element; Hyper mesh; Virtual Lab; Transmission lossCLC NO.: U467.4 Document Code: A Article ID: 1671-7988(2020)18-131-031 前言在进气系统前期开发阶段，流场仿真分析、声学仿真分析和结构模态仿真分析是设计和优化的主要依据。
基于Virtual.Lab Acoustics 的轿车乘员舱结构噪声分析
基于b Acoustics 的轿车乘员舱结构噪声分析周建文王晓光周舟长安汽车股份有限公司汽车工程研究院CAE所摘要:本文介绍了常用的声学边界元分析方法，并基于LMS b Acoustics软件，针对某轿车进行了车内声模态、驾驶员耳侧声压、面板贡献量分析PCA(Panel Contribution Analysis)、传递路径分析TPA(Transfer Path Analysis)、接附点导纳IPI(Input Point Inertance)等分析。
综合分析结果，找出了弱点，为车身等结构的改进提供了依据。
关键词:声模态声压 TPA PCA IPIAbstract: In this paper, the method of BEM analysis is introduced. Based on LMS b Acoustics, cab acoustic modes analysis, analysis of sound pressure at driver’s ear, PCA, TPA, IPI analysis of one car are performed. According to these results weaknesses are obtained and the work is helpful for improving the body structure of the car.Key words: acoustic mode, sound pressure, TPA, PCA, IPI1 概述噪声问题在汽车工业中已经引起了人们的普遍关注和重视，特别是近年来随着人们对轿车乘坐舒适性的要求越来越高，减振降噪已经成为汽车开发中越来越重要的环节。
因此，在汽车设计初期就预测车内振动噪声水平，提出有效减振降噪方案，可以大大的提高开发效率，降低开发成本。
乘员舱是典型的弹性薄壁腔体结构，其内部噪声除了由外部辐射噪声传入车内外，主要由壁板结构振动与车内空气产生强烈耦合作用引起的低频轰鸣噪声。
基于LMS Virtual.Lab Acoustics的抗性消声器性能分析研究
基于LMS b Acoustics的抗性消声器性能分析研
究
孙路伟;武秀东;海智渊;李伟龙
【期刊名称】《机械》
【年(卷),期】2014(000)005
【摘要】运用声学有限元软件LMS b中的Acoustics模块对具有内插管的抗性消声器内部声场进行有限元分析.通过划分消声器有限元网格、定义声学网格、前处理等一系列步骤对消声器的传递损失进行了理论计算,并且对比相关的有限元分析软件及实验结果,验证了声学有限元软件计算结果的准确性.为消音器的设计优化提供了理论基础.
【总页数】4页(P57-60)
【作者】孙路伟;武秀东;海智渊;李伟龙
【作者单位】长春理工大学机电工程学院,吉林长春130022;长春理工大学机电工程学院,吉林长春130022;长春理工大学机电工程学院,吉林长春130022;长春理工大学机电工程学院,吉林长春130022
【正文语种】中文
【中图分类】TB535+.2
【相关文献】
1.基于LMS virtual lab的抗性消声器声学性能研究及优化 [J], 许自顺;张强;咸凯;胡志睿
2.基于LMS b的起落架动态性能仿真分析 [J], 崔飞;马东立
3.基于b Acoustics的管道壁面声阻抗优化分析 [J], 郑伟光;许鹏;林泽宇;唐荣江;
4.LMS b Acoustic 9A版新功能 [J], 唐浩
5.基于LMS b的货车转向架疲劳性能仿真研究 [J], 马思群;孙凯;孙彦彬;聂春戈
因版权原因，仅展示原文概要，查看原文内容请购买。
（〈Virtual．LabAcoustics声学仿真计算高级应用实例》简介
（〈Virtual．LabAcoustics声学仿真计算高级应用实例》
简介
佚名
【期刊名称】《计算机辅助工程》
【年(卷),期】2010(19)4
【摘要】《Virtual．LabAcoustics声学仿真计算高级应用实例》于2010年8月由国防工业出版社出版，作者为李增刚、詹福良．全书共300页，由声学理论和高级应用实例构成．
【总页数】1页(P33-33)
【关键词】高级应用;声学理论;仿真计算;实例;国防工业;出版社
【正文语种】中文
【中图分类】TP393.092
【相关文献】
1.仿真软件Webench简介与应用实例 [J], 朱宁;谢瑞;何湘宁
2.一个基于高级仿真构架（HLA）的计算机仿真系统的设计 [J], 凌云翔;史湘宁
3.微计算机及其在核医学中的应用第六讲Appel Ⅱ 应用实例——γ心功能仪简介[J], 王秉湖;付强;焦琦平
4.微计算机及其在核医学中的应用第七讲Apple Ⅱ 的应用实例——γ心功能仪简介(二) [J], 王秉湖;付强;焦琦萍
5.基于Pro／E三维技术的冲压工艺计算高级应用实例 [J], 李焱
因版权原因，仅展示原文概要，查看原文内容请购买。
基于Virtual.Lab的汽车排气消声器性能仿真研究的开题报告
基于b的汽车排气消声器性能仿真研究的开题报告一、研究背景随着汽车产业的发展，汽车市场对汽车的噪声和排放标准越来越高。
其中，排气消声器是降低汽车噪声和排放的一种重要装置。
因此，对汽车排气消声器的研究与分析具有重要的意义。
目前，虚拟仿真技术已经成为汽车部件的设计和开发中的重要手段之一，因此，利用虚拟仿真技术开展汽车排气消声器性能仿真研究，具有重要的现实意义和应用价值。
二、研究内容与研究目标本研究将基于b软件平台，对汽车排气消声器的性能进行仿真研究，包括流场分析、声场分析和振动分析等方面。
具体研究内容如下：1.基于三维模型和有限体积法建立汽车排气消声器的物理模型；2.基于传热传质理论，分析消声器内部的流场特性；3.基于声学理论，分析消声器的声学性能；4.基于结构力学理论，分析消声器的振动特性；5.通过数值模拟与实验结果的比对和分析，验证b平台的计算精度和稳定性。
本研究的目标是，通过对汽车排气消声器性能的虚拟仿真分析，为汽车排气消声器的优化设计和性能改进提供基础和理论支持。
三、研究方法和技术路线1.建立汽车排气消声器的三维物理模型；2.进行流场分析，采用有限体积法求解流体动力学方程，计算消声器内部的流场特性；3.进行声学性能分析，采用有限元法求解声学方程，计算消声器的声学性能；4.进行振动分析，采用有限元法求解结构力学方程，计算消声器的振动特性；5.将流场、声学和振动分析的仿真结果进行综合，并与实验结果进行比较分析；6.得出汽车排气消声器性能优化方案，并进行仿真验证。
四、研究意义和创新点1.通过虚拟仿真技术分析研究汽车排气消声器的性能，为汽车排气消声器的优化设计和性能改进提供理论支持；2.利用b软件平台开展汽车排气消声器性能仿真分析，对该软件的计算精度和稳定性进行验证；3.通过仿真分析得出消声器的优化方案，为实际生产和应用中的汽车排气消声器提供更加优化的性能。
五、预期成果1.建立汽车排气消声器的三维可视化模型；2.对消声器内部的流场、声场和振动特性进行分析并提出优化方案；3.验证b软件平台在汽车排气消声器性能仿真分析方面的计算精度和稳定性；4.撰写汽车排气消声器性能仿真研究论文，并参加相关学术会议进行交流和分享；六、计划进度第一年：完成研究方案的设计和模型建立；第二年：完成流场分析和声学性能分析的仿真计算；第三年：完成振动分析的仿真计算，撰写成果论文并参加学术会议进行交流和分享。
- 1、下载文档前请自行甄别文档内容的完整性，平台不提供额外的编辑、内容补充、找答案等附加服务。
- 2、"仅部分预览"的文档,不可在线预览部分如存在完整性等问题,可反馈申请退款(可完整预览的文档不适用该条件!)。
- 3、如文档侵犯您的权益，请联系客服反馈,我们会尽快为您处理(人工客服工作时间：9:00-18:30)。
对于降低声源的噪声辐射，与制造业的水平有关，而且每降低1dB(A)耗资巨大。面对目前迫切亟需的噪声问题，无论从经济性还是从降噪效果上，声屏障都成为了不二之选。声屏障主要通过吸声材料对声波进行吸收、反射等一系列物理反应来降低到达受声点的声能量，平均可降低10～15dB(A)，且造价相对较为低廉。
国内研究概况：
(1)声屏障理论研究
2009年中南大学李文、吴小萍等[11,12]在探讨声屏障应该考虑的环境影响因素的基础上，提出把声屏障环境影响评价纳入环境影响评价（EIA）体系中，为解决声屏障建设发展过程中出现的问题提供参考。
(2)声屏障降噪效果研究
2013年西南交通大学周信、肖新标[13]等基于边界元理论，利用高速列车车外声源现场试验识别结果，建立考虑车体和轨道结构的高速铁路声屏障降噪效果预测模型，利用其计算无声屏障情况下车外声场特性和通用声屏障插入损失，并与试验结果比对，结果表明理论模型的预测结果与试验结果较吻合。
2.国内外发展及研究现状
国外研究概况：
(1)声屏障理论研究
L.Godinho[4,5]等用边界元法（BEM）评估了高层建筑附近无限长刚性声屏障对三维声源的散射情况，通过傅里叶变换得到时间信号，分析了不同大小声屏障对建筑物附近声压降低效果，并与简化算法得到的结果进行比较。
Ishizuka[6]等对具有不同形状和表面状态的声屏障隔声性能进行了测试。结果表明，吸声材料和柔性边缘能够显著提高声屏障的性能。
对噪声的控制方法一般可以从三部分来考虑：声源控制、传播途径控制以及受声点的防护；由于铁路噪声影响范围较广，影响对象也具有一定的离散性和流动性，对受影响的人群进行个人防护不仅成本较高，且影响正常生活，不切实际。因此，目前应用以及研究的噪声控制方法主要集中在声源的控制和传播途径控制。声屏障属于噪声控制中的传播途径控制，声屏障是噪声控制中最经济也是性价比最高的方法。其优越性体现在以下几个方面：
2.选题报告不通过者不得进入论文工作阶段。
3.双面打印或用黑色水笔双面填写，要求字迹清晰，文句通顺。
4.如有栏目填写不下可加附页
1.
截止2013年，我国投入运营的高速铁路里程达到9356公里，居世界第一位。高速铁路的建设极大缓和了各个地区资源分布不均的状况，满足了人们日益增长的出行要求，推动了沿线经济的快速发展。然而，高速铁路的快速发展也带来很多严重的环境问题。在我国第一次200km/h以上高速铁路论证会上，噪声污染被认为是高铁对社会产生的最大的环境污染因素[1]。一项对我国47个大中城市市区噪声的调查显示[2]，白天城市区域的平均声级为59dB(A)，夜间为49dB(A)，而铁路干线两侧噪声绝大部分超过70dB(A)，平均声级达76dB(A),当有列车经过时噪声更是达到了80dB(A)以上，这已经严重影响到了居民正常的生活和工作。世界卫生组织研究表明，噪声会不同程度地影响人的精神状态和身体健康，噪声除了会引起听觉疲劳、使人听力损伤甚至造成噪声性耳聋外，还会对人体的神经系统、消化系统以及视力等产生一定的影响，降低人们的生活质量和工作效率；此外，特别强烈的噪声还会对附近仪器设备和建筑物造成一定破坏。为了控制和缓解交通噪声的影响，《中华人民共和国城市区域环境噪声标准》[3]中明确规定了城市五类区域的环境噪声限值
(2)安装拆卸简便，占地较少
对于规划已经无法更改的老城区，住宅区的建筑也已成形，建专门屏障构造物来减少降噪的同时，能够有效的节约土地，且具有安装拆卸方便等优点。
(3)结构形式多样
随着高速铁路的快速发展，铁路噪声的干扰越来越大，为了有效降低噪声的影响，声屏障也演变出多种结构形式，如倒L型、Y型、半圆形及全封闭型等，能够满足不同程度的降噪需求，并从单一的治理效果逐步走向与景观协调一致的发展趋势。
(3)声屏障数值仿真模拟的研究
S.J.Martin[9]等使用二维边界元方法的波动方程和积分方程建模，第一个模型使用了连续的线声源，第二个模型使用了不连续的线声源，研究表明第一个模型与英国交通噪声预测得到的结果有较好的一致性，第二个模型预测的声屏障插入损失明显比第一个模型更高。
J.Forssen[10]等使用风和温度湍流强度来预测厚声屏障的插入损失，测量和预测之间的比较表明，该方法在中、高频段提供了相当准确的结果。
(2)声屏障降噪效果的研究
P.A.morgan[7]等研究了轨道边各种铁路隔音声屏障的降噪性能。结果表明：对于任何特定的形状，吸声性声屏障，提供比刚性声屏障更好的降噪效果。
W.Shao[8]等研究了不规则边缘声屏障的声学特性，对直边屏障和不规则边缘屏障的声学特性进行了比较，结果表明，随机边缘屏障可以产生比直边声屏障显著多的插入损耗。
3.
主要研究内容：
(1)提出研究方向
在大量阅读国内外文献的基础上，总结目前国内噪声污染的现状，从现有的控制方法中选取最为经济有效的降噪措施作为研究对象，通过分析国内外相关的研究中的不足，提出本文的研究方向。
(2)基本理论概述
对声屏障降噪的基本概念及原理进行阐述，并推导声屏障降噪效果评价指标的相关公式。介绍b Acoustics仿真理论及计算公式，并对数值仿真方法的有效性和准确性进行检验。
(3)声屏障数值仿真模拟的研究
2013年重庆交通大学陈永光、袁启慧[14]等通过对重庆某道路的交通噪声实地测量，结合声屏障的设计规范，设计出适合该区域的三种不同顶部结构的声屏障，并通过声学软b Acoustic对设计结果进行仿真研究。
通过国内外研究现状，我们可以看到，针对某一具体顶部结构，如倒L型声屏障的降噪效果仿真分析的研究较少，并且，在这里进一步对倒L型声屏障的折角进行研究探讨。
硕士研究生学位论文选题报告
论文题目
基于b Acoustics的倒L型声屏障降噪效果仿真分析
研究生姓名
王珂
学号
2015112019
导师姓名
石焕文
学科、专业
力学
研究方向
学院名称
理学院
选题报告时间
2017年3月15日
填表说明
1.选题报告是学位论文工作的重要组成部分，是中期考核筛选的重要内容。